Alvimopan dihydrate, chemically known as [[2(S)-[[4(R)-(3-hydroxyphenyl)-3(R),4-dimethyl-1-piperidinyl]methyl]-1-oxo-3-phenylpropyl]amino]acetic acid dihydrate is indicated to accelerate the time to upper and lower gastrointestinal recovery following partial large or small bowel resection surgery with primary anastomosis.
U.S. Pat. No. 6,242,635 B1 discloses the process for the preparation of (R)-2-benzyl-3-hydroxy propanoic acid which is as follows:

The above said process is having following disadvantages, which include:                Process for the preparation of compound of formula-III is critical and takes place 2-3 days for completion of the reaction.        Usage of raw material like methyl acrylate is not suggestible for use in laboratory as well as commercial scale process.        Usage of expensive palladium-carbon for the reduction of compound of formula-V and also resulted in the formation of undesired byproduct leading to decrease in yield of desired product and increases the cost of production.        The compound of formula-VI may require resolution to get the desired compound which may lead to the loss of unwanted enantiomer and provides the wanted enantiomer with 50% yield.        
As the above said process suffers from several drawbacks including use of inaccessible raw materials, expensive reagents and involving time consuming multi-step reaction sequences, lengthy procedure for the separation of isomers mixture involving column chromatographic purification's resulting in low yield of the desired product.
Hence, there is a need in the art to develop an improved, economical viable and efficient route for the preparation of (R)-2-benzyl-3-hydroxypropanoic acid that provides good yield with high enantionmeric purity of the desired compound as well as the yield and purity of [[2(S)-[[4(R)-(3-hydroxyphenyl)-3(R),4-dimethyl-1-piperidinyl]methyl]-1-oxo-3-phenylpropyl]amino]acetic acid dihydrate.